Enhancing Doxorubicin Bioavailability via Dissolving Microneedles: Roles of Drug Loading and Administration Force

To mitigate the severe adverse effects associated with the systemic administration of doxorubicin (DOX), this study developed a dissolving microneedles (MN) patch loaded with doxorubicin hydrochloride (DOX-MN) for the local treatment of breast cancer. It specifically investigated the influence and underlying mechanisms of drug loading and application force on drug bioavailability. DOX-MN with intact structure and drug enrichment at the needle tips were successfully fabricated using a centrifugal micro-molding technique. Characterization confirmed the excellent mechanical strength and skin insertion capability of the MN, which dissolved rapidly and released the drug within 30 min. In vivo pharmacokinetic studies identified drug loading and application force as critical determinants of bioavailability. A high drug loading potentially created a local supersaturated state, enhancing drug penetration and achieving a relative bioavailability of 65.25%. Increasing the application force to 25 N effectively minimized drug residue on the skin surface, improving bioavailability by approximately 1.5-fold. In a 4T1 tumor-bearing mouse model, DOX-MN administration facilitated efficient drug enrichment and sustained retention at the tumor site, yielding a tumor inhibition rate (90.61%) comparable to intravenous injection. Safety assessments indicated that using a dedicated applicator significantly reduced skin irritation. This study demonstrates that optimizing drug loading and application force enables efficient local DOX delivery via MN, ensuring potent antitumor efficacy while minimizing systemic toxicity, thereby presenting a promising novel strategy for breast cancer therapy.